1. Technical Field
This invention relates generally to a process for laminating a hologram to a substrate, and more specifically, to a process for laminating a hologram between two final product substrates without any other interfering support layers.
2. Discussion
The art of holography has come a long way since its early inception as a means to create a three-dimensional image. Today, the use of holograms has a wide range of commercial, as well as technologically advanced applications. One such application of a hologram is laminating the hologram between two layers of windshield glass to create a heads-up display for use in a vehicle, such as an automobile or aircraft. What this means is that a hologram carrying information of vehicle operation can be laminated within the windshield of the vehicle to enable the vehicle operator to receive the information and still maintain visual contact with his surroundings. Since the incorporation of a hologram in such a final laminated configuration generally includes not only the hologram itself, but a support substrate or backing layer on which the hologram was developed, the increased thickness due to these layers of the final laminate thickness offers certain drawbacks in the prior art.
To laminate the hologram and backing or support layer, the prior art hologram processing techniques generally includes the body of bonding technology which has applications to optical process technologies. The most relevant prior art is a technique employing a thin sheet of glass as an interlayer between a process substrate and a hologram, as shown generally in FIG. 1. In FIG. 1A, shown at 10 is an end view of a prior art laminated hologram after the hologram generating process has been completed. Laminate 10 includes a process substrate layer 12 generally of a glass material and having a thickness of about 0.125" (approximately 450 microns). Substrate layer 12 acts as a support layer on which a hologram 18 is developed by means well known to those skilled in the art. Hologram 18 will be approximately 25 microns thick. Adhered to substrate layer 12 is a microsheet 16 by means of an adhesive layer 14. Microsheet 16 is generally a glass having a thickness of approximately 75 microns. Adhesive 14 can be any known optical glue. Hologram 18 is developed on microsheet 16 opposite substrate 12 from a gelatin or photoemulsion layer.
After completion of the holographic process, hologram 18 and microsheet 16 are removed from the process substrate 12 by dissolving adhesive layer 14 or by peeling, each well known to those skilled in the art. The hologram 18 and microsheet 16 are then sandwiched between two final laminate substrates 11 and 13, such as a dual windshield glass configuration of an automobile, in their final product, as shown in FIG. 1B. Adhesive layers 15 and 17 provide the means by which the hologram/microsheet laminate is adhered to the windshield layers 11 and 13.
Because the final laminate includes the relatively thick microsheet (75 microns), the final thickness of the windshield is unnecessarily increased thus producing certain windshield deformations, and further, increasing optical distortion. Another problem arising is the extra handling required for removing the fragile hologram/microsheet laminate from the process substrate. This handling produces incidental optical defects, such as scratches, wrinkles, and particulate contamination. And finally, the hologram/microsheet is very flexible after it has been removed from the process substrate requiring high skill, and thus, the ability to efficiently and accurately transfer the hologram from the process substrate to the final laminate is difficult. These problems typically result in thickness gradients in the lamination, which produces optical distortion.
What is needed then is a hologram developing and lamination process which eliminates the need for the extra thickness of the prior art microsheet, and substantially eliminates the extra dexterity and handling required to position the thin hologram in its final lamination state.